Thermodynamics

Thermodynamics is the branch of science concerned with the nature of heat and its conversion to any form of energy. In thermodynamics, both the thermodynamic system and its environment are considered. A thermodynamic system, in general, is defined by its volume, pressure, temperature, and chemical make-up. In general, the environment will contain heat sources with unlimited heat capacity allowing it to give and receive heat without changing its temperature. Whenever the conditions change, the thermodynamic system will respond by changing its state; the temperature, volume, pressure, or chemical make-up will adjust accordingly in order to reach its original state of equilibrium. There are three laws of thermodynamics in which the changing system can follow in order to return to equilibrium.

In order for a system to gain energy the surroundings have to supply it, and visa versa when the system looses energy the surroundings must gain it. As the energy is transferred it can be converted form its original form to another as the transfer takes place, but the energy will never be created or destroyed. The first law of thermodynamics, also known as the law of conservation of energy, basically restates that energy can’t be destroyed or created “as follows: the total energy of the universe is a constant.” All around the conservation of energy is applied. When gasoline burns in the engine of a car, an equal amount of work and heat appear as the energy is released. The heat from the engine warms its surroundings, the cars parts, the air, and the passenger area. The heat energy is converted into the electrical energy of the radio, chemical energy of the battery, and radiant energy of the lights. The change in the sum of all of the energies formed from the burnt gasoline would be equal to the “…change in energy between the reactants and products.” Biological processes, like photosynthesis, also follow energy conservation. The green plants convert the radiant energy emitted by the Sun into useful chemical energy, such as the oxygen that we breathe. The energy transferred between any surroundings and any system can be in the form of various types of work, chemical, mechanical, radiant, electrical, or heat.

The second law of thermodynamics is expressed as a cycle that “all processes occur spontaneously in the direction that increases the entropy of the universe (system plus surrounding).” Entropy, the number of ways the components of a system can be rearranged without changing the system, plays a major roll in the second law of thermodynamics. This law was derived from the Carnot Cycle. Carnot observed that the “…flow of heat from higher to lower temperatures” motivates steam engines, like the flow of a steam turns the mill wheel. His key insight demonstrated that the world was always active, whenever there is an energy disruption that is out of equilibrium the “thermodynamic force” of the world will spontaneously act to bring the system back to equilibrium or to keep the disruption to a minimum. All changes seem to be motivated by this law. Unlike the first law, the second law changes and motivates change in all real world processes and expresses time, where as in the first law there is no time, there is nothing to distinguish past, present, and future. The second law, with its “one way flow” or cycle, allows for the possibility of a past, present, and future to exist there are no limitations on entropy. For example, if a cup of hot coffee is placed in a refrigerator, a potential exists and a flow of heat is spontaneously produced from the cup to the air in the refrigerator until the temperatures are the same and all flow will stop. Once the flow of heat stops the entropy is at its maximum. In all physical processes entropy will increase; “in ideal reversible processes entropy remains constant. Thus, in the Carnot cycle, which is reversible, there is no change in the total entropy.” The cup of coffee itself experiences no net change in the entropy because it is returned to its original state at the end of the cycle. The entropy gained by the cold refrigerator is equal to the entropy lost by the hot coffee cup.

The third law of thermodynamics is very much related to the second law. The third law, also know as the Nernst heat theorem, states “a perfect crystal has zero entropy at a temperature of absolute zero.” Perfect means that all of the particles are flawless and there are no defects of any kind. A statement that is related to but independent from the second law, is that it is impossible to cool a system to absolute zero by any processes. Absolute zero can be approached very closely, but can never actually be reached. The state is defined as having zero entropy only if it is perfect. In the real world where not much if perfect, this zero entropy may never be reached, but curtain objects may come really close. When the object approaches absolute zero the particles have the minimum amount of energy at this point, they are basically no longer moving. As the object is heated the molecules begin to move again and the entropy rises. All the values of standard entropies of elements and compounds at 25°C are based upon this third law third law of thermodynamics.

In the real world all strives for balance or equilibrium, everything from a chemical compound to human beings. Through the laws of thermodynamics, the process of returning to the equilibrium or balance from a disorder is demonstrated. These laws pertain to all systems, from the formation of the Solar System to the inner working of every human heart.

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